The Relational Language. Todd S. Bacastow January 2004. Relational Query Languages. Query languages Allow manipulation and retrieval of data from a database. Query Languages QLs not intended to be used for complex calculations. QLs support easy, efficient access to large data sets.
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Todd S. Bacastow
Two mathematical Query Languages form the basis for “real” languages (e.g. SQL), and for implementation:
Glue together allpossible combinations
Only tuples in both reln 1 and reln 2
Everything in reln 1 take away everything in reln 2
Everything in reln 1 plus reln 2
Store (SName, City)
PriceList (UPC, SName, Price)
Item (UPC, IName, Warranty)